What do we know about the 'terrestrial' surfaces of Jupiter, Saturn, Uranus and Neptune? In Arthur C. Clarke's 2001: A Space Odyssey he fancied the solid core of Jupiter was a diamond larger than our entire world. Have we learned anything about these planets surfaces from our various probes?

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Probes can't go very far because they loose their connections with the mother ship to relay those findings. Another problem is that the pressure increases very rapidly as the probe goes into the atmosphere.

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Have we learned anything about these planets surfaces from our various probes?

Two points need to be dealt with:1. We do not rely solely on probes to provide information on the interior.2. These planets do not really have surfaces.

Information Sources
In addition to probes, knowledge of the interior of the giant planets is derived from these sources:· Basic telescopic observation – do not underestimate what can be deduced about interiors from nothing more than determination of mass, rotation periods and polar and equatorial radii.· Experimentally derived data on the behaviour of materials at high pressure· Atmospheric composition derived from spectroscopic analysis

Probes fall into three categories: fly-by (Pioneer and Voyager); orbiting (Galileo and Cassinni); atmospheric (Galileo). In addition to high resolution telescopic observations of the atmosphere, the orbiters offer improved compositional information via spectroscopic analysis and (very importantly) data on the high order gravitational field of the planets.

Interiors
At the core of the giant planets there is thought to be a rocky component that, in the case of Jupiter, is around ten Earth masses. This may contain a significant proportion of ice. Above this lies a “sea” of liquid metallic hydrogen (with an admixture of helium) into the which the atmosphere blends imperceptibly. On theoretical grounds it is suspected that the transition from liquid hydrogen-helium to rock-ice core may be mixed. (Personally, given the order of magnitude density difference between the two zones, I find it intuitively difficult to accept, but the theory is beyond me to refute on technical grounds.)

Saturn is thought to be qualitatively comparable with Jupiter.

Uranus and Neptune lack the mass to generate the pressures to produce metallic hydrogen and are also much richer in compounds such as methane and ammonia and water. There interior is dominated by an ocean of these. Largely rocky cores are present, but lying at the bottom of such an alien ocean they would likely not offer surfaces as we would think of them.